1. Field of the Invention
The invention relates to a method for diamond turning of a metal mirror to have high precision, particularly a concave metal mirror of large diameter.
2. Description of the Prior Art
It has been heretofore customary for astronomical telescopes to use concave glass mirrors of large diameters. Manufacture of these concave glass mirrors necessitates glass blanks to be polished over long periods of time. This established practice, however, has suffered from the disadvantage that the work involved is both inefficient and costly.
The technique of diamond turning metal parts has recently advanced to the point where metal mirrors produced by this technique compare favorably with conventional optical mirrors produced from glass blanks. Thus, the advantage of metal mirrors over glass mirrors in terms of ease of handling, time required for work, and cost has come to be increasingly appreciated. Owing to the standard of the existing technique, however, high quality metal mirrors manufacturable today by this technique are limited in size to a maximum diameter of about 50 cm. Mirrors of increasingly large diameters, however, are now being demanded for use in laser nuclear fusion, solar heat power generation, atmospheric environment test, infrared telescope, and laser radar observation. Substantially all these mirrors of large diameters are concave mirrors which have spherical, parabolic, or hyperbolic reflecting surfaces. Production of concave mirrors of such large diameters with high precision by the work of turning is extremely difficult.